This invention relates to a rotary drill bit and drill bit cone for straight hole drilling through earth formations.
The concept of penetrating the surface of the earth to tap subterranean sources of water and minerals has been known for centuries. Within the last century, however, increased attention has been directed to earth boring to tap zones of fossel fuel such as gas and oil lying thousands of feet beneath the surface of the earth.
Drill bits which must function at such depths should be somewhat versatile and capable of penetrating a variety of earth strata without displaying excess wear and/or poor penetration rates.
One previously known drill bit design which has achieved a wide degree of utilization is generically known as a rotary drill bit. In this regard, a drill bit body is fitted with a plurality of rotatable cutting cones. The drill bit body is mounted at the end of a rotary drill string. As the drill body is rotated in a drill hole the cutting cones rotate relative to the bit and drill through earth formations. A drilling fluid or mud slurry is pumped down the drill string and is directed around and between the cutting cones to keep the cutting surfaces lubricated and to flush away particulate matter dislodged during the drilling operation.
A wide variety of rotary drill bit and cutting cone designs have been at least theorized in the past. In one design, a plurality of chisel shaped cutting teeth are mounted in layers about a cutting cone. Each layer is offset such that the tips of the chisel teeth form a general spiral pattern. In another design, spiral cutting edges are fashioned from the apex to the base of a rotatable cutting cone. Principally, however, rotary drill bits are provided with annular rows of generally rounded or "knob" like hardened inserts which serve to grind away an earth formation as the drill bit body is rotated.
While rotary drill bits of the general type previously described have been widely utilized, each of the previously known designs exhibit at least some limitations. More specifically, some rotary drill bits and cutting cones provide superior initial penetration rates but wear quickly. In order to replace a worn bit, the entire drill string must be pulled which necessarily dictates undesirable drilling down time. Other designs which exhibit increased bit wear properties sometimes do not provide an acceptable penetration rate and/or exhibit poor drilling performance in various earth strata. Still further, many previously known bit designs are easily clogged and difficult to keep clean, even with high drilling fluid flow rates, during a drilling operation.
The difficulties suggested in the preceding are not intended to be exhaustive, but rather are among many which may tend to reduce the effectiveness and operator satisfaction with prior rotary drill bits and drill bit cones. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that rotary drill bits and drill bit cones appearing in the past will admit to worthwhile improvement.